In the past, a customer purchasing custom software would expect to receive a copy of the application source code at the conclusion of the project. Owning the source code had a number of benefits including:

Documenting the work that was completed

Providing a way for the application to be modified in the future

Proof of ownership and a way to define intellectual property (patents, etc.)

Insurance in the event that the vendor could no longer support the application.

For some businesses, these reasons and others continue to be a motivation to negotiate and pay for source code rights. With the advent of Custom Software as a Service, the value of owning the source code is lower for many businesses. Why?

They have no in-house technical staff and cannot use the source code to make changes

The complexity of the application is too great and there it would require expensive and specialized skills to take advantage of the source code, even for experienced third-party programmers

The dramatically lower costs that are associated with Custom Software as a Service make it financially advantageous to "lease" functionality, rather than own it.